Electric discharge tube



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Patented Dec. 1 0, 1940 I ELECTRIC DISCHARGE TUBE Otto Louis vanSteenis, Eindhoven, Netherlands,

assignor, by mesne assignments, to Radio Corporation of America, NewYork, N. Y., a corporation'o! Delaware Application May 11, 1938, SerialNo. 207,276 In Germany May 14, 1937 6 Claims.

This invention relates to an electric discharge tube and moreparticularly, an electron discharge tube wherein is provided aluminescent screen adapted to be impacted by electrons. The

luminescent material may be applied on to a conductive or insulatingsubstratum which may be either provided as a separate member in the tubeor form part of the wall. Well-known representatives of this kind oftubes'are cathode ray tubes, tuning indicators and the like. Theinvention is more particularly concerned with electric discharge tubescomprising a fluorescent screen which consists of a material provided ona conductive substratum. In addition the invention relates to a methodof making such tubes. For these screens various materials have beenproposed. The most preferred and used material is willemite whichconsists of a mixture of zinc silicate and manganese oxide. Althoughgood results are often obtai led with this material its use togetherwith a conductive substratum may involve difiiculties. For the provisionand the use on a conductive substratum the fluorescent material, inorder not to reduce too much 2 the conductivity of such an electrode,must be applied in a very finely divided state and be very thin, whichmay be ensured by grounding the willemite for a long time until therequired degree of fineness has been attained. It is now Y 39 found thatupon 11. ng such screens the luminous intensity as a function of timerapidly decreases and attains a comparatively constant value after sometime which, however, is materially lower than the initial value.

35 I have found that upon using an electric discharge tube and a methodaccording to the present invention a fluorescent screen is obtainedwhose luminous intensity decreases only slightly with time and inaddition preserves a compara- 40 tively high value for a considerabletime.

In part this desirable feature is provided by supplying a screenincorporating the same material used in an electron emissive cathodeprovided within the envelope along with the'screen,

since poisoning is thereby avoided.

Accordingly, the main object of the invention is to provide anelectronic tube having an improved luminescent screen.

50 A further object of my invention is to provide method and means ofimproving luminescent screens by avoiding poisoning of the screen byproductsof cathode disintegration within an electric discharge tube.

5 Another object of my invention is to provide a new and improvedluminescent or fluorescent material.

A still further object of my invention is to provide a luminescentscreen comprising my new luminescent material deposited, upon a conduct-5 ing layer. 7

Other objects and features of my invention will become apparent uponreading the following detailed description together with the drawing inwhich I have shown schematically the end wall 10 of a cathode ray tubetogether with the conductive layer and the luminescent materialdeposited thereon.

Such a tube comprises a fluorescent screen, more particularly a screenfurnished with fiuol5 rescent material 5 applied on to a conductivesubstratum 3 supported upon the end wall of a cathode ray tube I. Anelectron gun, shown conventionaly as comprising a cathode I and an anode9, is mounted in the tube opposite the fiuo- 20 rescent screen to supplyelectrons from impacting the material to produce luminescence. Thismaterial essentially comprises one or more of the oxides of elements ofthe first series of group III of the periodic table, such as, barium,strontium or calcium to which a slight quantity of manganese dioxide hasbeen added. This mixture wherein the manganese dioxide acts as anactivator has a high and fairly constant luminous intensity for aconsiderable time. I have found that a mixture of 98% of strontium oxideand 2% of manganese dioxide gives excellent results.

We may preferably proceed as follows: A mixture of alkaline earthcarbonates such as strontium carbonate containing 2% of manganesecarbonate is precipitated, for instance, from a solution of thenitrates. If desired, this mixture is ground together with a smallquantity of an organic binder till therequired degree of fineness hasbeenattained, whereupon it is sprayed to form a thin layer on aconducting surface such as a plate consisting of nickel or similarmaterial. The electrode thus formed is subsequently located, togetherwith the other electrodes of the tube, inside the bulb and finally,after exhaustion, which may be efiected by high-frequency heating, thecarbonate mixture is decomposed into oxide.

Instead of starting with a mixture of the carbonates it is also possibleto use a mixture of 60 alkaline earth carbonate and manganese oxide. andto work them in the same manner as has been set out for the carbonatemixture.

A tube according to the invention has the advantage that when. uponusing a normal oxide cathode emitting material evaporates from thecathode towards the fluorescent, screen this screen is not poisonedthereby, because the substance transmitted by vaporization is the same aas that already present on the screen.

Having described my invention, what I claim is:

1. A luminescent screen comprising a supporting surface, a conductivelayer deposited upon said surface, and a fluorescent material formedfrom the reaction product resulting from a thermal treatment of amixture only of manganese dioxide and an oxide of an element chosen fromthe first series of the second group of the periodic table depositedupon said conductive layer.

2. An electron tube comprising an envelope having housed in one endthereof an electron gun having an electron emitting element formed fromat least one of the elements of the first series of group 2 of theperiodic tables, a conductive layer deposited upon the inner surface ofthe tube wall removed from the electron gun and in substantial alignmenttherewith, and a fluorescent material' formed from the reaction productresulting from a thermal treatment only of a mixture of manganesedioxide and an oxide of an element chosen from the first series of thesecond group of the periodic tables deposited upon said conductinglayer, whereby disintegration of the electron emitting material of theelectron gun becomes non-poisonous with respect to the fluorescentmaterial.

3. A cathode ray tube comprising an envelope having mounted upon one endthereof an electron emitting cathode formed from at least one of theelements of the first series of group II elements of the first series ofgroup II of the periodic system, and a luminescent screen comprising alayer of nickel supporting luminescent material formed from the thermaltreatment of a mixture of 2% of manganese dioxide and 98% of strontiumoxide, and an oxide'of an element chosen from the first series of thesecond group of the periodic system, said luminescent screen.

being positioned normal to said cathode.

5. A luminescent screen comprising a supporting surface, a conductivelayer deposited upon said surface, and a fluorescent material formedfrom the reaction product resulting from thermal treatment of a mixtureon the order of 98% of strontium oxide and on the order of 2% ofmanganese dioxide deposited upon said conductive layer.

6. A luminescent screen comprising a supporting surface and afluorescent material formed from the reaction product resulting from athermal treatment of a mixture only of manganese dioxide and an oxide ofan element chosen from the first series of the second group of theperiodic table deposited upon said supporting surface.

OTTO LOUIS VAN STEENIS.

